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A salt‐tolerant line of alfalfa (Medicago sativa L.) cells was selected for use in a comparative study examining the cellular traits associated with the capacity to tolerate salt. Suspension cultures of alfalfa cells were plated onto agarsolidified media containing 1% (w/v) NaCl. Within 2 months of exposure, more than 99% of these plated cells exhibited arrested growth and discoloration. A small number of cells exposed to salt, however, continued to grow and maintain a healthy appearance. These variants were subcultured onto media containing 1% NaCl every 3 to 4 weeks for 8 months. Several differences were observed between a salt‐selected cell line and a nonselected cell line from the original population in response to a gradient of NaCl concentrations in the nutrient media. Callus growth rates and ionic uptake by the cell lines differed. The selected line grew better than the unselected culture at high levels of NaCl, suggesting an increased NaCl tolerance. This selected line performed poorly in the absence of NaCl and the data suggest that it required a substantial amount of NaCl for optimal growth. A general shift towards a halophytic mode of salt tolerance within the salt‐selected cell line is suggested.

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Five mini-Tn5 derivatives encoding resistance to Km, Cm, Gm, Tc, and Sm, coupled with the polylinker of the pBluescriptII plasmid, were constructed. These derivatives are carried by an ampicillin-resistant plasmid that has a conditional origin of replication from plasmid R6K and origin of conjugal transfer from the broad host range plasmid RP4. The new vectors are smaller than those previously described and possess numerous unique restriction sites inside the minitransposons for gene cloning in addition to SfiI and NotI sites found in their predecessors.

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